Conventional wire-based LAN systems employ extensive fixed cabling to interconnect the multiple stations which form the networked system. The installation of such fixed cabling is difficult enough when performed concurrently with new building construction and is even more problematic when an existing structure must be retrofitted. In the resultant LAN using fixed cabling, the networked stations are constrained to installation at fixed locations which are dependent on such cabling.
To address these concerns and limitations, radio LANs have been developed which utilize wireless radio links rather than cable to interconnect the network stations. Unfortunately, radio based LANs encounter another set of problems unique to the indoor radio environment. For example, radio LANs are susceptible to multi-path fading which can interfere with inter-station communication.
FIG. 1 shows a conventional radio LAN including stations 1, 2, 3 . . . N which are interconnected by a radio link. These stations each include radio transmitting and radio receiving portions (not shown). A LAN station typically transmits information in frames such as frame 10 shown in FIG. 2. Frame 10 includes a preamble 12, a start delimiter 14 designated SD, a network identification designator number 16 (NWID), user data 18, and an end delimiter 20 designated ED. In the radio LAN environment, there is a need for synchronization during the reception of the frame in order to recover the user data. To facilitate such synchronization, the start delimiter SD is transmitted preceding the synchronization sensitive part of the frame. More specifically, symbol synchronization is required to receive the network identification number NWID and user data.
In a radio LAN environment, the transmitted frames can be received within a predetermined area around the transmitting station by any station using the same carrier frequency and the same modulation type. The use of NWID's makes the logical isolation of two or more LAN's possible on a physical level. In the case of overlapping and partially overlapping LAN's, the transmission medium can be effectively shared by using such NWID's. In this manner, the transmissions of the respective LAN's can be distinguished from one another.
In order for the respective stations in the radio LAN to maintain synchronization and to communicate reliably, it is required that relatively high quality radio communication links be maintained among the various stations of the network. For diagnostic purposes, it is desirable that a particular LAN station be able to analyze the conditions of transmission and reception between the particular LAN station and another station in the LAN. The quality of transmission and reception over a particular radio frequency (RF) path which forms the communication link is determined by several factors. For example, the presence of RF barriers such as wall and floors affect the integrity of the radio link. Delay spread distortion by reflections also affects signal quality over the link. Moreover, signal level and quality, hereinafter "link quality", is affected by antenna placement and the presence of interfering sources on the same radio frequency as employed by the link. For these reasons, measurement of RF path conditions between stations in the LAN is important to permit an assessment of the quality of wireless communications within the LAN.